Ionic conductivity and the formation of cubic CaH2 in the LiBH4-Ca(BH4)2 composite

Dadi Þorsteinn Sveinbjörnsson, Didier Blanchard, Jón Steinar Garðarsson Mýrdal, Reza Younesi, Rasmus Viskinde, Marit Dalseth Riktor, Poul Norby, Tejs Vegge

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Abstract

LiBH4–Ca(BH4)2 composites were prepared by ball milling. Their crystal structures and phase composition were investigated using synchrotron X-ray diffraction and Rietveld refinement, and their ionic conductivity was measured using impedance spectroscopy. The materials were found to form a physical mixture. The composites were composed of α-Ca(BH4)2, γ-Ca(BH4)2 and orthorhombic LiBH4, and the relative phase quantities of the Ca(BH4)2 polymorphs varied significantly with LiBH4 content. The formation of small amounts of orthorhombic CaH2 and cubic CaH2 in a CaF2-like structure was observed upon heat treatment. Concurrent formation of elemental boron may also occur. The ionic conductivity of the composites was measured using impedance spectroscopy, and was found to be lower than that of ball milled LiBH4. Electronic band structure calculations indicate that cubic CaH2 with hydrogen defects is electronically conducting. Its formation along with the possible precipitation of boron therefore has an effect on the measured conductivity of the LiBH4–Ca(BH4)2 composites and may increase the risk of an internal short-circuit in the cells.
Original languageEnglish
JournalJournal of Solid State Chemistry
Volume211
Pages (from-to)81-89
ISSN0022-4596
DOIs
Publication statusPublished - 2014

Keywords

  • Lithium borohydride
  • Calcium borohydride
  • Calcium hydride
  • Solid electrolyte
  • Ionic conductivity
  • X-ray diffraction

Cite this

Sveinbjörnsson, Dadi Þorsteinn ; Blanchard, Didier ; Mýrdal, Jón Steinar Garðarsson ; Younesi, Reza ; Viskinde, Rasmus ; Riktor, Marit Dalseth ; Norby, Poul ; Vegge, Tejs. / Ionic conductivity and the formation of cubic CaH2 in the LiBH4-Ca(BH4)2 composite. In: Journal of Solid State Chemistry. 2014 ; Vol. 211. pp. 81-89.
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abstract = "LiBH4–Ca(BH4)2 composites were prepared by ball milling. Their crystal structures and phase composition were investigated using synchrotron X-ray diffraction and Rietveld refinement, and their ionic conductivity was measured using impedance spectroscopy. The materials were found to form a physical mixture. The composites were composed of α-Ca(BH4)2, γ-Ca(BH4)2 and orthorhombic LiBH4, and the relative phase quantities of the Ca(BH4)2 polymorphs varied significantly with LiBH4 content. The formation of small amounts of orthorhombic CaH2 and cubic CaH2 in a CaF2-like structure was observed upon heat treatment. Concurrent formation of elemental boron may also occur. The ionic conductivity of the composites was measured using impedance spectroscopy, and was found to be lower than that of ball milled LiBH4. Electronic band structure calculations indicate that cubic CaH2 with hydrogen defects is electronically conducting. Its formation along with the possible precipitation of boron therefore has an effect on the measured conductivity of the LiBH4–Ca(BH4)2 composites and may increase the risk of an internal short-circuit in the cells.",
keywords = "Lithium borohydride, Calcium borohydride, Calcium hydride, Solid electrolyte, Ionic conductivity, X-ray diffraction",
author = "Sveinbj{\"o}rnsson, {Dadi {\TH}orsteinn} and Didier Blanchard and M{\'y}rdal, {J{\'o}n Steinar Gar{\dh}arsson} and Reza Younesi and Rasmus Viskinde and Riktor, {Marit Dalseth} and Poul Norby and Tejs Vegge",
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volume = "211",
pages = "81--89",
journal = "Journal of Solid State Chemistry",
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Ionic conductivity and the formation of cubic CaH2 in the LiBH4-Ca(BH4)2 composite. / Sveinbjörnsson, Dadi Þorsteinn; Blanchard, Didier; Mýrdal, Jón Steinar Garðarsson; Younesi, Reza; Viskinde, Rasmus; Riktor, Marit Dalseth; Norby, Poul; Vegge, Tejs.

In: Journal of Solid State Chemistry, Vol. 211, 2014, p. 81-89.

Research output: Contribution to journalJournal articleResearchpeer-review

TY - JOUR

T1 - Ionic conductivity and the formation of cubic CaH2 in the LiBH4-Ca(BH4)2 composite

AU - Sveinbjörnsson, Dadi Þorsteinn

AU - Blanchard, Didier

AU - Mýrdal, Jón Steinar Garðarsson

AU - Younesi, Reza

AU - Viskinde, Rasmus

AU - Riktor, Marit Dalseth

AU - Norby, Poul

AU - Vegge, Tejs

PY - 2014

Y1 - 2014

N2 - LiBH4–Ca(BH4)2 composites were prepared by ball milling. Their crystal structures and phase composition were investigated using synchrotron X-ray diffraction and Rietveld refinement, and their ionic conductivity was measured using impedance spectroscopy. The materials were found to form a physical mixture. The composites were composed of α-Ca(BH4)2, γ-Ca(BH4)2 and orthorhombic LiBH4, and the relative phase quantities of the Ca(BH4)2 polymorphs varied significantly with LiBH4 content. The formation of small amounts of orthorhombic CaH2 and cubic CaH2 in a CaF2-like structure was observed upon heat treatment. Concurrent formation of elemental boron may also occur. The ionic conductivity of the composites was measured using impedance spectroscopy, and was found to be lower than that of ball milled LiBH4. Electronic band structure calculations indicate that cubic CaH2 with hydrogen defects is electronically conducting. Its formation along with the possible precipitation of boron therefore has an effect on the measured conductivity of the LiBH4–Ca(BH4)2 composites and may increase the risk of an internal short-circuit in the cells.

AB - LiBH4–Ca(BH4)2 composites were prepared by ball milling. Their crystal structures and phase composition were investigated using synchrotron X-ray diffraction and Rietveld refinement, and their ionic conductivity was measured using impedance spectroscopy. The materials were found to form a physical mixture. The composites were composed of α-Ca(BH4)2, γ-Ca(BH4)2 and orthorhombic LiBH4, and the relative phase quantities of the Ca(BH4)2 polymorphs varied significantly with LiBH4 content. The formation of small amounts of orthorhombic CaH2 and cubic CaH2 in a CaF2-like structure was observed upon heat treatment. Concurrent formation of elemental boron may also occur. The ionic conductivity of the composites was measured using impedance spectroscopy, and was found to be lower than that of ball milled LiBH4. Electronic band structure calculations indicate that cubic CaH2 with hydrogen defects is electronically conducting. Its formation along with the possible precipitation of boron therefore has an effect on the measured conductivity of the LiBH4–Ca(BH4)2 composites and may increase the risk of an internal short-circuit in the cells.

KW - Lithium borohydride

KW - Calcium borohydride

KW - Calcium hydride

KW - Solid electrolyte

KW - Ionic conductivity

KW - X-ray diffraction

U2 - 10.1016/j.jssc.2013.12.006

DO - 10.1016/j.jssc.2013.12.006

M3 - Journal article

VL - 211

SP - 81

EP - 89

JO - Journal of Solid State Chemistry

JF - Journal of Solid State Chemistry

SN - 0022-4596

ER -